A commercial humic acid inhibits benzo(a)pyrene biodegradation by Paracoccus aminovorans HPD-2

Benzo(a)pyrene (BaP) is posing serious threats to soil ecosystems and its bioremediation usually limited by environmental factors and microbial activity. Humic acid (HA), a ubiquitous heterogeneous organic matter, which could affect the fate of environmental pollutants. However, the impact of HA on bioremediation of organic contamination remains controversial. In the present study, the biodegradation of BaP by Paracoccus aminovorans HPD-2 with and without HA was explored. Approximately 87.4 % of BaP was biodegraded in the HPD-2 treatment after 5 days of incubation, whereas the addition of HA dramatically reduced BaP biodegradation to 56.0 %. The limited BaP biodegradation in the HA + HPD-2 treatment was probably due to the decrease of BaP bioavailability which induced by the adsorption of HA with unspecific interactions. The excitation-emission matrix (EEM) of fluorescence characteristics showed that strain HPD-2 was responsible for the presence of protein-like substances and the microbial original humic substances in the HPD-2 treatment. Addition of HA would result in the increase of soluble microbial humic-like material, which should ascribe to the biodegradation of BaP and probably utilization of HA. Furthermore, both the growth and survival of strain HPD-2 were inhibited in the HA + HPD-2 treatment, because of the limited available carbon source (i.e. BaP) at the presence of HA. The expression of gene1789 and gene2589 dramatically decreased in the HA + HPD-2 treatment, and this should be responsible for the decrease of BaP biodegradation as well. This study reveals the mechanism that HA affect the BaP biodegradation, and the decrease of biodegradation should ascribe to the interaction of HA and bacterial strain. Thus, the bioremediation strategies of PAHs need to consider the effects of organic matter in environment.

Isolation and characterization of novel 3,3'-iminodipropionitrile biodegrading Paracoccus communis, from an industrial wastewater treatment bioreactor

Until now, bacteria able to degrade, 3,3'-iminodipropionitrile (IDPN), a neurotoxin that destroys vestibular hair cells, causing ototoxicity, culminating in irreversible movement disorders, had never been isolated. The aim of this study was to isolate a novel IDPN-biodegrading microorganism and characterize its metabolic pathway. Enrichment was performed by inoculating activated sludge from a wastewater treatment bioreactor that treated IDPN-contaminated wastewater in M9 salt medium, with IDPN as the sole carbon source. A bacterial strain with a spherical morphology that could grow at high concentrations was isolated on a solid medium. Growth of the isolated strain followed the Monod kinetic model. Based on the 16S rRNA gene, the isolate was Paracoccus communis. Whole-genome sequencing revealed that the isolated P. communis possessed the expected full metabolic pathway for IDPN biodegradation. Transcriptome analyses confirmed the overexpression of the gene encoding hydantoinase/oxoprolinase during the exponential growth phase under IDPN-fed conditions, suggesting that the enzyme involved in cleaving the imine bond of IDPN may promote IDPN biodegradation. Additionally, the newly discovered P. communis isolate seems to metabolize IDPN through cleavage of the imine bond in IDPN via nitrilase, nitrile hydratase, and amidase reactions. Overall, this study lays the foundation for the application of IDPN-metabolizing bacteria in the remediation of IDPN-contaminated environments.

Partial nitrification-denitrification and enrichment of paracoccus induced by iron-chitosan beads addition in an intermittently-aerated activated sludge system

Insufficient carbon source has become the main limiting factor for efficient nitrogen removal in wastewater treatment. In this study, an intermittently-aerated activated sludge system with iron-chitosan (Fe-CS) beads addition was proposed for nitrogen removal from low C/N wastewater. By adding Fe-CS beads, partial nitrification-denitrification (PND) process and significant enrichment of Paracoccus (with ability of iron reduction/ammonium oxidation/aerobic denitrification) were observed in the reactor. The accumulation rate of NO2--N reached 81.9 %, and the total nitrogen removal efficiency was improved to 93.9 % by shortening the aeration time. The higher activity of ammonium oxidizing bacteria and inhibited activity of nitrite-oxidizing bacteria in Fe-CS assisted system mediated the occurrence of PND. In contrast, the traditional nitrification and denitrification process occurred in the control group. The high-throughput sequencing analysis and metagenomic results confirmed that the addition of Fe-CS induced 77.8 % and 54.9 % enrichment of Paracoccus in sludge and Fe-CS beads, respectively, while almost no enrichment was observed in control group. Furthermore, with the addition of Fe-CS beads, the expression of genes related to outer membrane porin, cytochrome c, and TCA was strengthened, thereby enhancing the electron transport of Fe(Ⅱ) (electron donor) and Fe(Ⅲ) (electron acceptor) with pollutants in the periplasm. This study provides new insights into the direct enrichment of iron-reducing bacteria and its PND performance induced by the Fe-CS bead addition. It therefore offers an appealing strategy for low C/N wastewater treatment.

Biodegradation efficiency and mechanism of erythromycin degradation by Paracoccus versutus W7

Continuous and excessive usage of erythromycin results in serious environmental pollution and presents a health risk to humans. Biological treatment is considered as an efficient and economical method to remove it from the environment. In this study, a novel erythromycin-degrading bacterial strain, W7, isolated from sewage sludge was identified as Paracoccus versutus. Strain W7 degraded 58.5% of 50 mg/L erythromycin in 72 h under the optimal conditions of 35 °C, pH 7.0, and 0.1% sodium citrate with yeast powder in mineral salt medium. It completely eliminated erythromycin from erythromycin fermentation residue at concentrations of 100 and 300 mg/L within 36 and 60 h, respectively. Erythromycin esterase (EreA) was found to be involved in erythromycin metabolism in this strain and was expressed successfully. EreA could hydrolyze erythromycin, and its maximum activity occurred at pH 8.5 and 35 °C. Finally, six intermediates of erythromycin degraded by strain W7 were detected by high performance liquid chromatography mass spectrometry. Based on the novel intermediates and enzymes, we determined two possible pathways of erythromycin degradation by strain W7. This study broadened our understanding of the erythromycin catabolic processes of P. versutus and developed a feasible microbial strategy for removing erythromycin from erythromycin fermentation residue, wastewater, and other erythromycin-contaminated environments.

Thermal Endurance by a Hot-Spring-Dwelling Phylogenetic Relative of the Mesophilic Paracoccus

High temperature growth/survival was revealed in a phylogenetic relative (SMMA_5) of the mesophilic Paracoccus isolated from the 78 to 85°C water of a Trans-Himalayan sulfur-borax spring. After 12 h at 50°C, or 45 min at 70°C, in mineral salts thiosulfate (MST) medium, SMMA_5 retained ~2% colony forming units (CFUs), whereas comparator Paracoccus had 1.5% and 0% CFU left at 50°C and 70°C, respectively. After 12 h at 50°C, the thermally conditioned sibling SMMA_5_TC exhibited an ~1.5 time increase in CFU count; after 45 min at 70°C, SMMA_5_TC had 7% of the initial CFU count. 1,000-times diluted Reasoner's 2A medium, and MST supplemented with lithium, boron, or glycine-betaine, supported higher CFU-retention/CFU-growth than MST. Furthermore, with or without lithium/boron/glycine-betaine, a higher percentage of cells always remained metabolically active, compared with what percentage formed single colonies. SMMA_5, compared with other Paracoccus, contained 335 unique genes: of these, 186 encoded hypothetical proteins, and 83 belonged to orthology groups, which again corresponded mostly to DNA replication/recombination/repair, transcription, secondary metabolism, and inorganic ion transport/metabolism. The SMMA_5 genome was relatively enriched in cell wall/membrane/envelope biogenesis, and amino acid metabolism. SMMA_5 and SMMA_5_TC mutually possessed 43 nucleotide polymorphisms, of which 18 were in protein-coding genes with 13 nonsynonymous and seven radical amino acid replacements. Such biochemical and biophysical mechanisms could be involved in thermal stress mitigation which streamline the cells' energy and resources toward system-maintenance and macromolecule-stabilization, thereby relinquishing cell-division for cell-viability. Thermal conditioning apparently helped inherit those potential metabolic states which are crucial for cell-system maintenance, while environmental solutes augmented the indigenous stability-conferring mechanisms. IMPORTANCE For a holistic understanding of microbial life's high-temperature adaptation, it is imperative to explore the biology of the phylogenetic relatives of mesophilic bacteria which get stochastically introduced to geographically and geologically diverse hot spring systems by local geodynamic forces. Here, in vitro endurance of high heat up to the extent of growth under special (habitat-inspired) conditions was discovered in a hot-spring-dwelling phylogenetic relative of the mesophilic Paracoccus species. Thermal conditioning, extreme oligotrophy, metabolic deceleration, presence of certain habitat-specific inorganic/organic solutes, and potential genomic specializations were found to be the major enablers of this conditional (acquired) thermophilicity. Feasibility of such phenomena across the taxonomic spectrum can well be paradigm changing for the established scopes of microbial adaptation to the physicochemical extremes. Applications of conditional thermophilicity in microbial process biotechnology may be far reaching and multifaceted.

Bioconversion of waste activated sludge hydrolysate into polyhydroxyalkanoates using Paracoccus sp. TOH: Volatile fatty acids generation and fermentation strategy

The expensive carbon matrix is a bottleneck restricting the industrialization of polyhydroxyalkanoates (PHAs). Volatile fatty acids (VFAs) derived from waste activated sludge via anaerobic fermentation might be alternative carbon matters for PHAs synthesis. In this study, the effect of enzymes on VFAs yields and the feasibility of the produced VFAs for PHAs fermentation by Paracoccus sp. TOH were investigated. The optimum cumulative VFAs concentration reached 4076.6 mg-COD·L^-1 in the lysozyme treatment system. Correspondingly, the highest poly(3-hydroxybuturate-co-3-hydroxyvalerate) (PHBV) concentration (119.1 mg·L^-1) containing 20.3 mol% 3-hydroxyvalerate was obtained. It proved that Paracoccus sp. TOH possesses the capability for PHBV accumulation. The functional hydrolytic-acidogenic microorganisms, such as Clostridium sensu stricto and Bacteroides sp. were accumulated. The functional genes encoding hydrolysis, carbohydrates metabolism, VFAs generation were enriched. This study offered a possible strategy for VFAs production and verified the feasibility of sludge hydrolysate as a high-quality carbon substrate for PHAs fermentation.

Characterisation of a potential probiotic strain Paracoccus marcusii KGP and its application in whey bioremediation

Whey, the main by-product obtained from the manufacture of cheese, which contains a very high organic load (mainly due to the lactose content), is not easily degradable and creates concern over environmental issues. Hydrolysis of lactose present in whey and conversion of whey lactose into valuable products such as bioethanol, sweet syrup, and animal feed offers the possibility of whey bioremediation. The increasing need for bioremediation in the dairy industry has compelled researchers to search for a novel source of β-galactosidase with diverse properties. In the present study, the bacterium Paracoccus marcusii KGP producing β-galactosidase was subjected to morphological, biochemical, and probiotic characterisation. The bacterial isolate was found to be non-pathogenic and resistant to low pH (3 and 4), bile salts (0.2%), salt (10%), pepsin (at pH 3), and pancreatin (at pH 8). Further characterisation revealed that the bacteria have a good auto-aggregation ability (40% at 24 h), higher hydrophobicity (chloroform-60%, xylene-50%, and ethyl acetate-40%) and a broad spectrum of antibiotic susceptibility. The highest growth of P. marcusii KGP was achieved at pH 7 and 28 °C, and the yeast extract, galactose, and MgSO₄ were the best for the growth of the bacterial cells. The bacterium KGP was able to utilise whey as a substrate for its growth with good β-galactosidase production potential. Furthermore, the β-galactosidase extracted from the isolate KGP could hydrolyse 47% whey lactose efficiently at 50 °C. The study thus reveals the potential application of β-galactosidase from P. marcusii KGP in whey bioremediation.

Conserved Pigment Profiles in Phylogenetically Diverse Symbiotic Bacteria Associated with the Corals Montastraea cavernosa and Mussismilia braziliensis

Pigmented bacterial symbionts play major roles in the health of coral holobionts. However, there is scarce knowledge on the diversity of these microbes for several coral species. To gain further insights into holobiont health, pigmented bacterial isolates of Fabibacter pacificus (Bacteroidetes; n = 4), Paracoccus marcusii (Alphaproteobacteria; n = 1), and Pseudoalteromonas shioyasakiensis (Gammaproteobacteria; n = 1) were obtained from the corals Mussismilia braziliensis and Montastraea cavernosa in Abrolhos Bank, Brazil. Cultures of these bacterial symbionts produced strong antioxidant activity (catalase, peroxidase, and oxidase). To explore these bacterial isolates further, we identified their major pigments by HPLC and mass spectrometry. The six phylogenetically diverse symbionts had similar pigment patterns and produced myxol and keto-carotene. In addition, similar carotenoid gene clusters were confirmed in the whole genome sequences of these symbionts, which reinforce their antioxidant potential. This study highlights the possible roles of bacterial symbionts in Montastraea and Mussismilia holobionts.

Toxicity of deltamethrin to Eriocheir sinensis and the isolation of a deltamethrin-degrading bacterium, Paracoccus sp. P-2

Deltamethrin is used widely in Eriocheir sinensis aquaculture to remove wild fish and parasites. The residual deltamethrin greatly affects the growth and quality of E. sinensis. In this study, the LC₅₀ of deltamethrin against E. sinensis at 24, 48 and 96 h was determined to be 6.5, 5.0 and 2.8 μg/L, respectively. The enzyme activity and gene transcription of SOD, CAT, and PO in the hepatopancreas of E. sinensis after deltamethrin stimulation showed an increasing tendency, and these enzymes reached their maximum activities at 6-10 d. The MDA content accumulated with increased time of deltamethrin stress. After 15 d of deltamethrin stress, the hepatopancreas of E. sinensis was found to be damaged based on HE staining. These results showed that deltamethrin is highly toxic to E. sinensis. But the half-life of deltamethrin is long and mainly relies on biodegradation. To resolve the pollution of residual deltamethrin, a strain of deltamethrin-degrading bacteria, P-2, was isolated from the sediment of an E. sinensis culture pond. Through morphological observation, physiological and biochemical identification and 16S rDNA sequence analysis, we found that this strain belonged to Paracoccus sp. When the pH was 7, the substrate concentration was low, the inoculation amount was high, and the deltamethrin degradation effect of Paracoccus sp. P-2 was good. The deltamethrin residue in the hepatopancreas and muscle of E. sinensis decreased significantly when Paracoccus sp. P-2 was added at 6.0 × 10⁸ CFU/L. The degradation efficiency of Paracoccus sp. P-2 in the hepatopancreas and muscle was more than 70%. These results showed that Paracoccus sp. P-2, the first deltamethrin-degrading bacterium in aquaculture, could be used to remove residual deltamethrin and improve the food safety of E. sinensis.

Involvement of membrane vesicles in long-chain-AHL delivery in Paracoccus species

Bacteria are known to communicate with each other through signalling molecules that regulate gene expression within the population. However, the way in which hydrophobic signals are released and transmitted among bacterial population is not well understood. Recent studies show that membrane vesicles (MVs) are involved in delivering hydrophobic signals, such as in N-hexadecanoyl-l-homoserine lactone (C16-HSL) signalling in Paracoccus denitrificans Pd1222. In this study, we identified the AHLs produced in Paracoccus aminophilus JCM7686, Paracoccus aminovorans NBRC16711, Paracoccus thiocyanatus JCM20756, Paracoccus versutus JCM20754 and Paracoccus yeei ATCC BAA-599, and show that the main AHL produced in all the strains is C16-HSL. Our results show that these Paracoccus species also release MVs that carry C16-HSL, but at different proportions. Most of the strains carry C16-HSL in MVs, while in P. aminophilus JCM7686, very little C16-HSL was detected in MVs, but was found in other fractions of the supernatant. Given the utilization of a common signal, we showed that these Paracoccus species can share signals with P. denitrificans Pd1222, and examined the role of MVs in signalling. Our study provides new insights into the way in which bacteria communicate using hydrophobic signals.

Current Approaches to and Future Perspectives on Methomyl Degradation in Contaminated Soil/Water Environments

Methomyl is a broad-spectrum oxime carbamate commonly used to control arthropods, nematodes, flies, and crop pests. However, extensive use of this pesticide in agricultural practices has led to environmental toxicity and human health issues. Oxidation, incineration, adsorption, and microbial degradation methods have been developed to remove insecticidal residues from soil/water environments. Compared with physicochemical methods, biodegradation is considered to be a cost-effective and ecofriendly approach to the removal of pesticide residues. Therefore, micro-organisms have become a key component of the degradation and detoxification of methomyl through catabolic pathways and genetic determinants. Several species of methomyl-degrading bacteria have been isolated and characterized, including Paracoccus, Pseudomonas, Aminobacter, Flavobacterium, Alcaligenes, Bacillus, Serratia, Novosphingobium, and Trametes. The degradation pathways of methomyl and the fate of several metabolites have been investigated. Further in-depth studies based on molecular biology and genetics are needed to elaborate their role in the evolution of novel catabolic pathways and the microbial degradation of methomyl. In this review, we highlight the mechanism of microbial degradation of methomyl along with metabolic pathways and genes/enzymes of different genera.

Transient-state operation of an anoxic biotrickling filter for H2S removal

The application of an anoxic biotrickling filter (BTF) for H₂S removal from contaminated gas streams is a promising technology for simultaneous H₂S and NO₃^- removal. Three transient-state conditions, i.e. different liquid flow rates, wet-dry bed operations and H₂S shock loads, were applied to a laboratory-scale anoxic BTF. In addition, bioaugmentation of the BTF with a H₂S removing-strain, Paracoccus MAL 1HM19, to enhance the biomass stability was investigated. Liquid flow rates (120, 60 and 30 L d^-1) affected the pH and NO₃^- removal efficiency (RE) in the liquid phase. Wet-dry bed operations at 2-2 h and 24-24 h reduced the H₂S elimination capacity (EC) by 60-80%, while the operations at 1-1 h and 12-12 h had a lower effect on the BTF performance. When the BTF was subjected to H₂S shock loads by instantly increasing the gas flow rate (from 60 to 200 L h^-1) and H₂S inlet concentration (from 112 (± 15) to 947 (± 151) ppm_v), the BTF still showed a good H₂S RE (>93%, EC of 37.8 g S m^-3 h^-1). Bioaugmentation with Paracoccus MAL 1HM19 enhanced the oxidation of the accumulated S⁰ to sulfate in the anoxic BTF.

Crystal structures of AztD provide mechanistic insights into direct zinc transfer between proteins

Zinc acquisition from limited environments is critical for bacterial survival and pathogenesis. AztD has been identified as a periplasmic or cell surface zinc-binding protein in numerous bacterial species. In Paracoccus denitrificans, AztD can transfer zinc directly to AztC, the solute binding protein for a zinc-specific ATP-binding cassette transporter system, suggesting a role in zinc acquisition and homeostasis. Here, we present the first cry stal structures of AztD from P. denitrificans and tbe human pathogen Citrobacter koseri, revealing a beta-propeller fold and two high-affinity zinc-binding sites that are highly conserved among AztD homologs. These structures combined with transfer assays using WT and mutant proteins provide rare insight into the mechanism of direct zinc transfer from one protein to another. Given the importance of zinc import to bacterial pathogenesis, these insights may prove valuable to the development of zinc transfer inhibitors as antibiotics.

Aerobic denitrification by Paracoccus sp. YF1 in the presence of Cu(II)

This study of Cu(II)'s impact on aerobic denitrification of Paracoccus sp. YF1 revealed that the denitrification rate decreased markedly from 99.8%, 98.0%, 68.7% to 16.3% when the concentrations of Cu(II) rose from 0, 0.01 mM, 0.05 mM to 0.1 mM, respectively. This outcome was confirmed by the successful test of OD₆₀₀, total protein and enzyme activities. As the concentration of Cu(II) increased from 0 to 0.1 mM, the total protein contents declined over a period of 48 h, and the activities of nitrate reductase (NR) and nitrite reductase (NIR) decreased remarkably during the first 24 h in a NO₃^- sufficient state. Meanwhile, the reduction of NO₃^- and NO₂^- was positively correlated with the expression level of NR and NIR. The removal rate of nitrate in the control treatment and different concentration of Cu(II) treatment fitted approximately to the zero-order model. Scanning electron microscopy (SEM) confirmed that the cell surfaces of Paracoccus sp. YF1 were disrupted when exposed to 0.1 mM Cu(II). The adsorption of Cu(II) onto the cells' surface was confirmed by Energy dispersive spectrometer (EDS), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy analysis (XPS). The insights obtained here regarding the influence of Cu(II) on aerobic denitrification will be of great significance for the treatment of heavy metals and nitrite co-existing sewage.

Paracoccus indicus sp. nov., isolated from surface seawater in the Indian Ocean

Strain IO390502^T, isolated from surface seawater in the Indian Ocean, was characterised using a polyphasic taxonomy approach. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain IO390502^T belongs to the genus Paracoccus and is closely related to Paracoccus seriniphilus DSM 14827^T (97.6%), followed by P. zeaxanthinifaciens JCM 21774^T (97.5%), P. homiensis DSM 17862^T (97.3%), P. marcusii DSM 11574^T (97.2%), P. haeundaensis BC 74171^T (97.0%) and P. carotinifaciens E-396^T (97.0%). Cells are Gram-negative, aerobic, poly-β-hydroxybutyrate-accumulating, motile, rod-shaped, and forms creamy-white colonies. Optimal growth occurred at 25-30 °C, pH 5-8, and in the presence of 3-8% NaCl. The genome of strain IO390502^T has a G+C content of 64.9 mol% and a 3.5 Mb chromosome. The in silico DNA-DNA hybridisation and average nucleotide identity values between strain IO390502^T and the three closely related taxa, P. seriniphilus DSM 14827^T, P. zeaxanthinifaciens JCM 21774^T and P. homiensis DSM 17862^T, are 19.6%, 21.9% and 20.6%, and 76.0%, 79.9% and 77.8%, respectively. Phosphatidylglycerol is the major lipid present, ubiquinone-10 (Q-10) is the sole isoprenoid quinone, and the major cellular fatty acid is C_18:1ω7c. Based on data from phenotypic tests and genotypic differences between strain IO390502^T and its close phylogenetic relatives, strain IO390502^T represents a new species belonging to the genus Paracoccus, for which the name Paracoccus indicus sp. nov. is proposed. The type strain is IO390502^T (= JCM 32637^T = CCTCC AB 2018071^T).

Effects of astaxanthin-rich dried cell powder from Paracoccus carotinifaciens on carotenoid composition and lipid peroxidation in skeletal muscle of broiler chickens under thermo-neutral or realistic high temperature conditions

Thirty-two 15-day old broiler chicks (Chunky strain ROSS 308) were randomly divided into four treatments in a 2 × 2 factorial design. The main factors were diet (basal diet or basal diet supplemented with 0.15% astaxanthin-rich dried cell powder (Panaferd-P [astaxanthin 30 ppm]) and ambient temperature (thermo-neutral [25 ± 1°C] or high [35 ± 1°C for 6 hr]). Dietary supplementation with Panaferd-P did not affect growth performance, though high ambient temperature decreased feed intake and the weight of breast tender muscle, liver, and heart. High ambient temperature also decreased redness in both breast and leg muscles of chickens, while Panaferd-P increased redness and yellowness of breast and leg muscles of chickens. Panaferd-P increased Paracoccus carotinifaciens-derived pigments (i.e., adonixanthin, astaxanthin, adonirubin, and cantaxanthin) as well as corn-derived pigments such as zeaxanthin and lutein in breast and leg muscles. High ambient temperature increased the malondialdehyde (MDA) concentration in breast muscle, while Panaferd-P decreased the MDA concentration in breast muscle under both temperature conditions. Our results suggest that dietary supplementation with Panaferd-P increases muscle carotenoid content, the redness and yellowness of meat and decreases the muscle MDA concentration in broiler chickens kept under thermo-neutral or high ambient temperature conditions.

Influencing mechanisms of hematite on benzo(a)pyrene degradation by the PAH-degrading bacterium Paracoccus sp. Strain HPD-2: insight from benzo(a)pyrene bioaccessibility and bacteria activity

Iron oxides are reactive inorganic soil components that play an important role in the fate and transport of organic pollutants. Here, hematite was selected to investigate its effect on the biodegradation of benzo[a]pyrene (BaP) by Paracoccus sp. strain HPD-2. Approximately 60% of the total BaP was degraded in the absence of hematite after 7 days but only 30.8 and 20.8% of that was degraded after the addition of 10 and 20 mg  mL^-1 hematite, respectively, indicating that the addition of hematite could significantly inhibit the biodegradation of BaP (P < 0.05). The hematite also lowered bacterium activity by coating the cells and by generating reactive oxygen species that destroyed the cells. Two-photon confocal laser scanning microscope images showed that the addition of hematite substantially decreased the amount of BaP combined with the bacterium, and this also enabled us to observe directly the migration and regression of BaP in the interaction between HPD-2 and hematite. Higher death ratio of HPD-2 might lower the BaP access to live cells because dead cells have a higher adsorption affinity for BaP than live cells. These observations enhance our understanding of the mechanisms by which metal oxides, organic pollutants and degrading-bacteria interact during the biodegradation process.

Biodegradation and utilization of dimethylformamide by biofilm forming Paracoccus sp. strains MKU1 and MKU2

Two bacterial strains capable of degrading N,N-dimethylformamide (DMF) were isolated from the effluent and sludge samples of textile and tyre industries. The 16S rRNA gene analysis revealed that bacterial strains belonged to the genera Paracoccus and named as Paracoccus sp. MKU1 and Paracoccus sp. MKU2. The DMF degradation experiments conducted at a DMF concentration of 1% v/v and HPLC analysis revealed that MKU1 and MKU2 degraded 55% and 46% of DMF after 120 h of growth. Biofilm quantification by microtiter plate assay revealed that both the bacterial isolates can form efficient biofilm on during DMF utilization. The presence of secondary carbon sources influenced the DMF degradation and biofilm formation where highest biofilm formation was observed in the presence of acetate and enhanced the DMF degradation to a maximum of 86.59% with MKU1 whereas glucose and acetate enhanced DMF degradation by MKU2 to a maximum of 82.7% and 80% respectively.

Evaluation of simultaneous nitrification and denitrification under controlled conditions by an aerobic denitrifier culture

Paracoccus versutus LYM was characterized with the ability of simultaneous nitrification and denitrification (SND) in presence of NH4(+)-N and NO3(-)-N (140mg/L-N each). However, there was approximate 95.80mg/L NO2(-)-N left during SND process. Fe(2+) was added in the SND medium and it benefited bacterial growth and further converted NO2(-)-N a little. Besides, remaining NO2(-)-N could be completely reduced by adding carbon donors in presence of NH4(+)-N and NO3(-)-N, whose converting efficiencies also reached 97.09% and 96.34%, respectively. And N2 stayed as the main product of SND process. While NO2(-)-N and NH4(+)-N were present simultaneously, strain LYM could also remove nitrogen compounds thoroughly with sufficient carbon source. But there was no NO2(-)-N reduced as sole nitrogen source in the medium even if C/N ratio reached as high as 30.

Influence of zero-valent iron nanoparticles on nitrate removal by Paracoccus sp

Nitrate contamination in drinking water is a major threat to public health. This study investigated the efficiency of denitrification of aqueous solutions in the co-presence of synthesized nanoscale zero-valent iron (nZVI; diameter: 20-80 nm) and a previously isolated Paracoccus sp. strain YF1. Various influencing factors were studied, such as oxygen, pH, temperature, and anaerobic corrosion products (Fe(2+), Fe(3+) and Fe3O4). With slight toxicity to the strain, nZVI promoted denitrification efficiency by providing additional electron sources under aerobic conditions. For example, 50 mg L(-1) nZVI increased the nitrate removal efficiency from 66.9% to 85.2%. However, a high concentration of nZVI could lead to increased production of Fe(2+), a toxic ion which could compromise the removal efficiency. Kinetic studies suggest that denitrification by both free cells, and nZVI-amended cells fitted well to the zero-order model. Temperature and pH are the major factors affecting nitrate removal and cell growth, with or without the presence of nZVI. In this study, nitrate removal and cell growth increased in the pH range of 6.5-8.0, and temperature range of 25-35 °C. These conditions favor the growth of the strain, which dominated denitrification in all scenarios involved. As for anaerobic corrosion products, compared with Fe(2+) and Fe(3+), Fe3O4 promoted denitrification by serving as an electron donor. Finally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) confirmed attachments of nZVI on the surface of the cell, and the formation of iron oxides. This study indicated that, as an electron donor source with minimal cellular toxicity, nZVI could be used to promote denitrification efficiency under biotic conditions.

Revealing biogenic sulfuric acid corrosion in sludge digesters: detection of sulfur-oxidizing bacteria within full-scale digesters

Biogenic sulfuric acid corrosion (BSA) is a costly problem affecting both sewerage infrastructure and sludge handling facilities such as digesters. The aim of this study was to verify BSA in full-scale digesters by identifying the microorganisms involved in the concrete corrosion process, that is, sulfate-reducing (SRB) and sulfur-oxidizing bacteria (SOB). To investigate the SRB and SOB communities, digester sludge and biofilm samples were collected. SRB diversity within digester sludge was studied by applying polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) targeting the dsrB-gene (dissimilatory sulfite reductase beta subunit). To reveal SOB diversity, cultivation dependent and independent techniques were applied. The SRB diversity studies revealed different uncultured SRB, confirming SRB activity and H2S production. Comparable DGGE profiles were obtained from the different sludges, demonstrating the presence of similar SRB species. By cultivation, three pure SOB strains from the digester headspace were obtained including Acidithiobacillus thiooxidans, Thiomonas intermedia and Thiomonas perometabolis. These organisms were also detected with PCR-DGGE in addition to two new SOB: Thiobacillus thioparus and Paracoccus solventivorans. The SRB and SOB responsible for BSA were identified within five different digesters, demonstrating that BSA is a problem occurring not only in sewer systems but also in sludge digesters. In addition, the presence of different SOB species was successfully associated with the progression of microbial corrosion.

Plasmids of carotenoid-producing Paracoccus spp. (Alphaproteobacteria) - structure, diversity and evolution

Plasmids are components of many bacterial genomes. They enable the spread of a large pool of genetic information via lateral gene transfer. Many bacterial strains contain mega-sized replicons and these are particularly common in Alphaproteobacteria. Considerably less is known about smaller alphaproteobacterial plasmids. We analyzed the genomes of 14 such plasmids residing in 4 multireplicon carotenoid-producing strains of the genus Paracoccus (Alphaproteobacteria): P. aestuarii DSM 19484, P. haeundaensis LG P-21903, P. marcusii DSM 11574 and P. marcusii OS22. Comparative analyses revealed mosaic structures of the plasmids and recombinational shuffling of diverse genetic modules involved in (i) plasmid replication, (ii) stabilization (including toxin-antitoxin systems of the relBE/parDE, tad-ata, higBA, mazEF and toxBA families) and (iii) mobilization for conjugal transfer (encoding relaxases of the Mob_Q, Mob_P or Mob_V families). A common feature of the majority of the plasmids is the presence of AT-rich sequence islets (located downstream of exc1-like genes) containing genes, whose homologs are conserved in the chromosomes of many bacteria (encoding e.g. RelA/SpoT, SMC-like proteins and a retron-type reverse transcriptase). The results of this study have provided insight into the diversity and plasticity of plasmids of Paracoccus spp., and of the entire Alphaproteobacteria. Some of the identified plasmids contain replication systems not described previously in this class of bacteria. The composition of the plasmid genomes revealed frequent transfer of chromosomal genes into plasmids, which significantly enriches the pool of mobile DNA that can participate in lateral transfer. Many strains of Paracoccus spp. have great biotechnological potential, and the plasmid vectors constructed in this study will facilitate genetic studies of these bacteria.

Biological removal of nitrate and ammonium under aerobic atmosphere by Paracoccus versutus LYM

The bacterium isolated from sea sludge Paracoccus versutus LYM was characterized with the ability of aerobic denitrification. Strain LYM performs perfect activity in aerobically converting over 95% NO3(-)-N (approximate 400mg L(-1)) to gaseous products via nitrite with maximum reduction rate 33 mg NO3(-)-N L(-1) h(-1). Besides characteristic of aerobic denitrification, strain LYM was confirmed in terms of the ability to be heterotrophic nitrification and aerobic denitrification (HNAD) with few accumulations of intermediates. After the nitrogen balance and enzyme assays, the putative nitrogen pathway of HNAD could be NH4(+) → NH2OH → NO2(-)→ NO3(-), then NO3(-) was denitrified to gaseous products via nitrite. N2 was sole denitrification product without any detection of N2O by gas chromatography. Strain LYM could also simultaneously remove ammonium and additional nitrate. Meanwhile, the accumulated nitrite had inhibitory effect on ammonium reduction rate.

Disintegration of aerobic granules: role of second messenger cyclic di-GMP

Loss of structural stability of aerobic granular process is the challenge for its field applications to treat wastewaters. The second messenger, cyclic diguanylate (c-di-GMP), is widely used by bacteria to regulate the synthesis of exopolysaccharide. This study for the first time confirmed the correlation between concentration of intracellular c-di-GMP and the granular stability under sequencing batch reactor (MBR) mode. In the presence of manganese ions (Mn(2+)), the concentrations of intracellular c-di-GMP and of extracellular polysaccharides and proteins in granules were declined. Clone library study revealed that the polysaccharide producers. Acinetobacter sp., Thauera sp., Bdellovibrio sp. and Paracoccus sp. were lost after Mn(2+) addition. The findings reported herein confirmed that the c-di-GMP is a key chemical factor epistatic to quorum sensing to determine granular stability. Stimulation of synthesis of intracellular c-di-GMP presents a potential way to enhance long-term stability of aerobic granules.

Effective and characteristics of anthraquinone-2,6-disulfonate (AQDS) on denitrification by Paracoccus versutus sp.GW1

The effects of anthraquinone-2,6-disulfonate (AQDS) on microbial populations and the biocatalysing characteristics of AQDS on denitrifying strain GW1 are discussed. The results showed that microbial population abundances were 30, 6, 12 and 18% during the different periods (1st, 5th, 10th and 20th days). Strain GW1 utilized AQDS as an electron acceptor in the respiration chain and reduced AQDS to hydroquinone (QH2). The nitrate removal efficiency of strain GW1 was increased 1.14-1.63 fold with 0.04-0.32 mmol/L AQDS. A linear correlation was found between the nitrate removal reaction constant k[gNO3(-)- N/(gVSS x d)] (where VSS is volatile suspended solids) and AQDS concentration (CAQDS), which was k = 19.332 C(AQDS) + 11.115 (R2 = 0.9749). The stabilized oxidation-reduction potential (ORP) values with AQDS were lower 22-92 mv than the control during the denitrification process. The concentration of nitrite sequentially accumulated up to around 250 mg/L when nitrate have removed completely. The results suggested that AQDS as redox mediator was capable of biocatalysing the nitrate and nitrite removal rate.

Study the catalyzing mechanism of dissolved redox mediators on bio-denitrification by metabolic inhibitors

The effect of dissolved redox mediators on denitrification by Paracoccus versutus sp. GW1 were studied with α-AQS, AQS, 1,5-AQDS, AQDS and 2,7-AQDS. AQDS presented the best catalytic effect which increased denitrification rate by 1.5-fold with 0.17 mmol L(-1). Denitrification rate was found to be pseudo-zero order with 0-0.32 mmol L(-1) AQDS (k=19.874C AQDS+10.301 (R(2)=0.9984)). The accelerating mechanism for respiratory chain was also explored by using metabolic inhibitors. Addition of AQDS eased the inhibitions of rotenone, dicumarol, sodium azide on respiratory chain, and enhanced the nitrite accumulation during bio-denitrification process. AQDS exhibited slight catalytic effect on nitrite denitrification. These results allowed us to deduce the accelerating site of AQDS on the denitrification respiratory chain. Increased nitrate denitrification by AQDS might mainly attribute to the accelerated electrons transfer from NADH to nitrate reductase via complex I and ubiquinone/ubiqunol. This study provided further understanding of the mechanism of redox mediators on denitrification.

Fe(II)EDTA-NO reduction coupled with Fe(II)EDTA oxidation by a nitrate- and Fe(III)-reducing bacterium

The nitrate- and Fe(III)-reducing bacterium Paracoccus versutus LYM was characterized in terms of its ability to perform Fe(II)EDTA-NO reduction coupled with Fe(II)EDTA oxidation (NO-dependent Fe(II)EDTA oxidation, NDFO). It experienced a single anaerobic FeEDTA redox cycling through NDFO and dissimilatory Fe(III)EDTA reduction in FeEDTA culture. The increase in the Fe(II)EDTA concentration contributed to the ascending Fe(II)EDTA-NO reduction rate. The amount of glucose controlled the rate and extent of Fe(II) oxidation during NDFO. Without glucose addition, Fe(II)EDTA-NO reduction rate was at a rather slow rate even in presence of relatively sufficient Fe(II)EDTA. Unlike aqueous Fe(2+) and solid-phase Fe(II), Fe(II)EDTA could prevent cells from encrustations. These findings suggested the occurrence of NDFO preferred being beneficial via a mixotrophic physiology in the presence of an organic cosubstrate to being out of consideration for metabolic strategy.

Remediation of polycyclic aromatic hydrocarbon and metal-contaminated soil by successive methyl-β-cyclodextrin-enhanced soil washing-microbial augmentation: a laboratory evaluation

Polycyclic aromatic hydrocarbon (PAH) and metal-polluted sites caused by abandoned coking plants are receiving wide attention. To address the associated environmental concerns, innovative remediation technologies are urgently needed. This study was initiated to investigate the feasibility of a cleanup strategy that employed an initial phase, using methyl-β-cyclodextrin (MCD) solution to enhance ex situ soil washing for extracting PAHs and metals simultaneously, followed by the addition of PAH-degrading bacteria (Paracoccus sp. strain HPD-2) and supplemental nutrients to treat the residual soil-bound PAHs. Elevated temperature (50 °C) in combination with ultrasonication (35 kHz, 30 min) at 100 g MCD L(-1) was effective in extracting PAHs and metals to assist soil washing; 93 % of total PAHs, 72 % of Cd, 78 % of Ni, 93 % of Zn, 84 % of Cr, and 68 % of Pb were removed from soil after three successive washing cycles. Treating the residual soil-bound PAHs for 20 weeks led to maximum biodegradation rates of 34, 45, 36, and 32 % of the remaining total PAHs, 3-ring PAHs, 4-ring PAHs, and 5(+6)-ring PAHs after washing procedure, respectively. Based on BIOLOG Ecoplate assay, the combined treatment at least partially restored microbiological functions in the contaminated soil. The ex situ cleanup strategy through MCD-enhanced soil washing followed by microbial augmentation can be effective in remediating PAH and metal-contaminated soil.

Degradation of piperazine by Paracoccus sp. TOH isolated from activated sludge

Piperazine is widely used as an intermediate in the manufacture of insecticides, rubber chemicals, corrosion inhibitors, and urethane. In this study, a highly effective piperazine-degrading bacteria strain, TOH, was isolated from the acclimated activated sludge of a pharmaceutical plant. This strain, identified as Paracoccus sp., utilises piperazine as the sole source of carbon, nitrogen and energy for growth. The optimal pH and temperature for the growth of TOH were 8.0 and 30°C, respectively. The effects of co-substrates and heavy metals on the degradation efficiency of piperazine were investigated. The results indicated that exogenously supplied glucose promoted the degradation of piperazine, while the addition of ammonium chloride slightly inhibited piperazine degradation. Metal ions such as Ni(2+) and Cd(2+) inhibited the degradation of piperazine, whereas Mg(2+) increased it. In addition, metabolic intermediates were identified by mass spectrometry, allowing a degradation pathway for piperazine to be proposed for the first time.

An L-glucose catabolic pathway in Paracoccus species 43P

BACKGROUND

L-Glucose, the enantiomer of D-glucose, was believed not to be utilized by any organisms.

RESULTS

An L-glucose-utilizing bacterium was isolated, and its L-glucose catabolic pathway was identified genetically and enzymatically.

CONCLUSION

L-Glucose was utilized via a novel pathway to pyruvate and D-glyceraldehyde 3-phosphate.

SIGNIFICANCE

This might lead to an understanding of homochirality in sugar metabolism. An L-glucose-utilizing bacterium, Paracoccus sp. 43P, was isolated from soil by enrichment cultivation in a minimal medium containing L-glucose as the sole carbon source. In cell-free extracts from this bacterium, NAD(+)-dependent L-glucose dehydrogenase was detected as having sole activity toward L-glucose. This enzyme, LgdA, was purified, and the lgdA gene was found to be located in a cluster of putative inositol catabolic genes. LgdA showed similar dehydrogenase activity toward scyllo- and myo-inositols. L-Gluconate dehydrogenase activity was also detected in cell-free extracts, which represents the reaction product of LgdA activity toward L-glucose. Enzyme purification and gene cloning revealed that the corresponding gene resides in a nine-gene cluster, the lgn cluster, which may participate in aldonate incorporation and assimilation. Kinetic and reaction product analysis of each gene product in the cluster indicated that they sequentially metabolize L-gluconate to glycolytic intermediates, D-glyceraldehyde-3-phosphate, and pyruvate through reactions of C-5 epimerization by dehydrogenase/reductase, dehydration, phosphorylation, and aldolase reaction, using a pathway similar to L-galactonate catabolism in Escherichia coli. Gene disruption studies indicated that the identified genes are responsible for L-glucose catabolism.

Removal of nitrate using Paracoccus sp. YF1 immobilized on bamboo carbon

Paracoccus sp. strain YF1 immobilized on bamboo carbon was developed for the denitrification. The results show that denitrification was significantly improved using immobilized cells compared to that of free cells, where denitrification time decreased from 24h (free cells) to 15 h (immobilized cells). The efficiency of denitrification increased from 4.57 mg/(Lh) (free cells) to 6.82 mg/(Lh) (immobilized cells). Kinetics studies suggest that denitrification by immobilized YF1 cells fitted well to the zero-order model. Scanning electron microscopy (SEM) demonstrated that firstly, the bacteria became stable on the inside and exterior of the bamboo carbon particles and secondly, they formed biofilm after adhesion. Various factors and their influences on biological denitrification were investigated, namely temperature, pH, initial nitrate concentrations and carbon sources. The immobilized cells exhibited more nitrate removal at various conditions compared to free cells since bamboo carbon as a carrier protects cells against changes in environmental conditions. Denitrification using the YF1 immobilized in bamboo carbon was also maintained 99.8% after the tenth cycle reuse, thus demonstrating excellent reusability. Finally, wastewater was treated using the immobilized cells and the outcome was that nitrogen was completely removed by bamboo-immobilized YF1.

[Biocatalyst of redox mediators on the denitrification by Paracoccus versutus strain GW1]

The quinone respiration process of Paracoccus versutus strain GW1 was characterized and the effects of the four redox mediators on the denitrification process were studied. The experiment results suggested that quinones were utilized by Paracoccus versutus strain GW1 as electron acceptors in the respiratory chain and reduced to hydroquinone. Batch experiments were carried out to investigate the biocatalyst effect of redox mediators as catalyst on the denitrification process at 35 degrees C. All four redox mediators tested were able to enhance the nitrate removal efficiency and the denitrification efficiency by 1.14-1.63 fold and 1.12-2.02 fold, respectively. The accelerating effect from high to low was AQDS > 1,5-AQDS > AQS > alpha-AQS. In the presence of redox mediators, the stabilized ORP values in the nitrate decomposition process were reduced by 33-75 mV. The pH variations in denitrification with redox mediators showed similar tendency to that of the conventional nitrate removal process. In the concentration range of 0-0.32 mmol x L(-1), AQDS had the best accelerating effect and a linear correlation was found for the denitrification rate K and the AQDS concentration cAQDS. This study indicated that the application of redox mediators significantly improved the denitrification process by enhancing the decomposition rate.

[Bioaugmented removal of pyridine and the microbial community dynamic analysis]

The bioaugmented removal of pyridine was investigated through introducing immobilized Paracoccus sp. strain KT-5 capable of degrading pyridine into the lab-scale sequencing batch reactor (SBR) inoculated with activated sludge. The terminal restriction fragment length polymorphisms (T-RFLP) was used to analyzed the microbial community dynamics of two reactors during the whole operation process. The experimental results indicated that the introduction of immobilized strain KT-5 into the SBR could speed up the start-up of reactor, compared to the non-bioaugmented SBR. When the initial concentration of pyridine varied from 195.6 mg x L(-1) to 586.8 mg x L(-1), the bioaugmented effect was not significant; however, when the initial concentration of pyridine was 782.4-2934 mg x L(-1), the bioaugmentation role in pyridine degradation was obvious. The analysis of T-RFLP indicated that the introduced immobilized strain KT-5, as a dominant strain, always existed in both free and immobilized biomass of the bioaugmented SBR.

Biodegradation of fipronil by Paracoccus sp. in different types of soil

In the present studies potential of microorganisms isolated from the cotton fields was explored for the bioremediation of fipronil contaminated soils. The cultures of microbes were grown in Luria broth as shake culture maintained at 28°C. After that Dorn's broth enrichment culture supplemented with fipronil was used and isolated two bacterial cultures viz. Paracoccus sp. and Gamma Proteobacteria. The performance of both bacteria was evaluated for degradation of fipronil in soil. Paracoccus sp. was found better than the Gamma Proteobacteria as far as degradation of fipronil in soil is concerned. The samples of soil were extracted and cleaned up by following a standardized methodology. Fipronil was quantified by gas liquid chromatography and confirmed by gas chromatography mass spectrometer. The limit of quantification of fipronil was worked out to be 10 μg kg(-1). By using this methodology, the mean recoveries of fipronil in different types of soil were found to be more than 85%. The residues of fipronil were found to persist only up to 10 days in soils fortified with fipronil @ 20 μg kg(-1) and amended with Paracoccus sp. while in the soils fortified @ 80 μg kg(-1) fipronil, residues persisted up to 20, 30 and 30 days in loamy sand, sandy loam and clay loam, respectively. Therefore, the use of Paracoccus sp. can further be explored for the bioremediation of fipronil contaminated soils.

Methyl-beta-cyclodextrin enhanced biodegradation of polycyclic aromatic hydrocarbons and associated microbial activity in contaminated soil

The contamination of soils by polycyclic aromatic hydrocarbons (PAHs) is a widespread environmental problem and the remediation of PAHs from these areas has been a major concern. The effectiveness of many in situ bioremediation systems may be constrained by low contaminant bioavailability due to limited aqueous solubility or a large magnitude of sorption. The objective of this research was to evaluate the effect of methyl-beta-cyclodextrin (MCD) on bioaugmentation by Paracoccus sp. strain HPD-2 of an aged PAH-contaminated soil. When 10% (W/W) MCD amendment was combined with bioaugmentation by the PAH-degrading bacterium Paracoccus sp. strain HPD-2, the percentage degradation of total PAHs was significantly enhanced up to 34.8%. Higher counts of culturable PAH-degrading bacteria and higher soil dehydrogenase and soil polyphenol oxidase activities were observed in 10% (W/W) MCD-assisted bioaugmentation soil. This MCD-assisted bioaugmentation strategy showed significant increases (p < 0.05) in the average well color development (AWCD) obtained by the BIOLOG Eco plate assay, Shannon-Weaver index (H) and Simpson index (lambda) compared with the controls, implying that this strategy at least partially restored the microbiological functioning of the PAH-contaminated soil. The results suggest that MCD-aided bioaugmentation by Paracoccus sp. strain HPD-2 may be a promising practical bioremediation strategy for aged PAH-contaminated soils.

Nitrate-dependent degradation of acetone by Alicycliphilus and Paracoccus strains and comparison of acetone carboxylase enzymes

A novel acetone-degrading, nitrate-reducing bacterium, strain KN Bun08, was isolated from an enrichment culture with butanone and nitrate as the sole sources of carbon and energy. The cells were motile short rods, 0.5 to 1 by 1 to 2 μm in size, which gave Gram-positive staining results in the exponential growth phase and Gram-negative staining results in the stationary-growth phase. Based on 16S rRNA gene sequence analysis, the isolate was assigned to the genus Alicycliphilus. Besides butanone and acetone, the strain used numerous fatty acids as substrates. An ATP-dependent acetone-carboxylating enzyme was enriched from cell extracts of this bacterium and of Alicycliphilus denitrificans K601(T) by two subsequent DEAE Sepharose column procedures. For comparison, acetone carboxylases were enriched from two additional nitrate-reducing bacterial species, Paracoccus denitrificans and P. pantotrophus. The products of the carboxylase reaction were acetoacetate and AMP rather than ADP. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of cell extracts and of the various enzyme preparations revealed bands corresponding to molecular masses of 85, 78, and 20 kDa, suggesting similarities to the acetone carboxylase enzymes described in detail for the aerobic bacterium Xanthobacter autotrophicus strain Py2 (85.3, 78.3, and 19.6 kDa) and the phototrophic bacterium Rhodobacter capsulatus. Protein bands were excised and compared by mass spectrometry with those of acetone carboxylases of aerobic bacteria. The results document the finding that the nitrate-reducing bacteria studied here use acetone-carboxylating enzymes similar to those of aerobic and phototrophic bacteria.

[Screening and identification of two heterotrophic nitrifying bacteria and characterization of their capacity for nitrogen removal]

OBJECTIVE

Two heterotrophic nitrifying bacteria, P2 and P9 isolated from piggery wastewater, were studied for their capacity of nitrification and nitrogen removal.

METHODS

Physiological characteristics and phylogenetic analysis based on 16S rDNA sequences of strains P2 and P9 were analyzed. The ammonia removal characteristics of strains P2 and P9 were investigated. Furthermore, nitrogen removal ability of strains P2 and P9 individually or mixed were evaluated in the treatment of actual piggery wastewater.

RESULTS

Strains P2 and P9 were identified as Paracoccus sp. and Shinella sp., respectively. Heterotrophic nitrification could occur by the strains when they utilized organics. After cultivation of 24 h, the ammonia removal rates by the strains were up to 80% approximately; meanwhile, there was almost no nitrite and nitrate accumulation. However, aerobic denitrification could not occur by the strains when NO3- or NO2- was provided as the sole nitrogen source, respectively. For heterotrophic nitrification, with strains P2 and P9, the optimal carbon source was sodium succinate, and the optimal C/N ratio was 9. Besides, the pH values rose from 6.8 to 8.9 in the whole ammonia removal process. The growth and nitrogen removal ability of the two strains depended much on the quantity of small molecule carbon source, and the nitrogen removal capability of strains P2 or P9 in wastewater with small molecule carbon source was improved evidently. The effect was strengthened especially when the two strains were mixed together.

CONCLUSION

Nitrogen removal ability of strains P2 and P9 was relatively strong, and they may exhibit broad application prospects in wastewater treatment.

Biodegradation of chloroacetamide herbicides by Paracoccus sp. FLY-8 in vitro

A butachlor-degrading strain, designated FLY-8, was isolated from rice field soil and was identified as Paracoccus sp. Strain FLY-8 could degrade and utilize six chloroacetamide herbicides as carbon sources for growth, and the degradation rates followed the order alachlor > acetochlor > propisochlor > butachlor > pretilachlor > metolachlor. The influence of molecular structure of the chloroacetamide herbicides on the microbial degradation rate was first analyzed; the results indicated that the substitutions of alkoxymethyl side chain with alkoxyethyl side chain greatly reduced the degradation efficiencies; the length of amide nitrogen's alkoxymethyl significantly affected the biodegradability of these herbicides: the longer the alkyl was, the slower the degradation efficiencies occurred. The phenyl alkyl substituents have no obvious influence on the degradation efficiency. The pathway of butachlor complete mineralization was elucidated on the basis of the results of metabolite identification and enzyme assays. Butachlor was degraded to alachlor by partial C-dealkylation and then converted to 2-chloro-N-(2,6-dimethylphenyl)acetamide by N-dealkylation, which subsequently transformed to 2,6-diethylaniline, which was further degraded via the metabolites aniline and catechol, and catechol was oxidized through an ortho-cleavage pathway. This study highlights an important potential use of strain FLY-8 for the in situ bioremediation of chloroacetamide herbicides and their metabolite-contaminated environment.

Biodegradation of pyridine by Paracoccus sp. KT-5 immobilized on bamboo-based activated carbon

The performance of pyridine degradation by Paracoccus sp. strain KT-5 immobilized on bamboo-based activated carbon was investigated and compared with that of free cells. The results showed that Paracoccus sp. was able to attach well on the surface and pores of bamboo-carbon. Compared with freely suspended cells, the pyridine-degrading rate of the immobilized cells was higher when initial pyridine concentration was in the range of 489-1476 mg/L, suggesting that the efficiency of pyridine degradation by Paracoccus sp. strain KT-5 was enhanced significantly by immobilization technique. Additionally, the attached biomass on the bamboo-carbon increased from 391.9 to 430-500 mg/g during pyridine degradation. Furthermore, the semi-continuous degradation of pyridine by immobilized cells were carried out when the pyridine concentration was in the range of 293-1476 mg/L, the results demonstrated the feasibility and reusability of immobilized cells for pyridine degradation.

Effect of bioaugmentation by Paracoccus sp. strain HPD-2 on the soil microbial community and removal of polycyclic aromatic hydrocarbons from an aged contaminated soil

A microcosm study was conducted to test the bioremediation potential of Paracoccus sp. strain HPD-2 on an aged PAH-contaminated soil. Bioaugmented microcosms showed a 23.2% decrease in soil total PAH concentrations after 28days, with a decline in average concentration from 9942 to 7638microg kg(-1) dry soil. The percentage degradation of 3-, 4- and 5(+6)-ring PAHs was 35.1%, 20.7% and 24.3%, respectively. Higher counts of culturable PAH-degrading bacteria, microbial biomass and enzyme activities were observed in bioaugmented soil. The bioaugmented microcosms showed significant increases (p<0.05) in the average well-color development (AWCD) obtained by the BIOLOG ecoplate assay and Shannon-Weaver index (H) compared to the controls. Principal component analysis of BIOLOG data clearly differentiated between the bioaugmented and control microcosms, implying that bioaugmentation restored the microbiological functioning of the PAH-contaminated soil. The results suggest that bioaugmentation by Paracoccus sp. strain HPD-2 may be a promising bioremediation strategy for aged PAH-contaminated soils.

Microbial degradation of pyridine by Paracoccus sp. isolated from contaminated soil

A pyridine-degrading strain was isolated from the contaminated soil near the pesticide plant, identified as Paracoccus sp., and designated as strain KT-5, on the basis of its partial 16S rRNA gene sequence analysis. The effect of different co-substrates including glucose, ammonium chloride and trace elements on biodegradation of pyridine by Paracoccus sp. KT-5 was investigated. The results showed that when the initial concentration of pyridine was about 900 mg L(-1), 100 mg L(-1) of glucose increased the growth of strain KT-5 and the removal of pyridine, but did not affect the release of nitrogen in the pyridine ring as ammonia. In addition, strain KT-5 was able to utilize 100 mg L(-1) of glucose and 900 mg L(-1) of pyridine simultaneously as the carbon source. 100 mg L(-1) of ammonium chloride inhibited the growth of strain KT-5 in 900 mg L(-1) of pyridine, and also slightly decreased the removal of pyridine, but did not affect the release of nitrogen in the pyridine ring as ammonia. However, lacking of trace elements not only inhibited the growth of strain KT-5 in 900 mg L(-1) of pyridine, but also decreased the removal of pyridine, while it did not affect the release of nitrogen in the pyridine ring as ammonia.

Biomineralization of N,N-dimethylformamide by Paracoccus sp. strain DMF

N,N-dimethylformamide (DMF) is a man-made compound that is widely used as a solvent for the synthesis of various organic compounds. In this study, a bacterial strain Paracoccus sp. DMF capable of using DMF as the sole carbon, nitrogen and energy source, was isolated from an enrichment culture developed using activated sludge from domestic waste water treatment unit as the source inoculum. The strain DMF was characterized by biochemical tests and 16S rDNA sequence analysis, to be belonging to the genus Paracoccus. Growth on DMF was accompanied with ammonia release and the total organic carbon (TOC) analysis indicated its extensive mineralization. Batch culture studies were conducted in the substrate range of 100-5000 mg L(-1) to determine the biokinetic constants. Strain Paracoccus sp. DMF could tolerate very high concentrations of DMF as the growth was observed even at 15000 mg L(-1). High (micro(max)) and (K(i)) showed the suitability of the strain for the treatment of DMF containing waste water. Transient accumulation of dimethylamine (DMA) in the medium during the growth on DMF and utilization of DMA and monomethylamine (MMA) as growth substrates by Paracoccus sp. strain DMF showed that the pathway of DMF degradation involves DMA and MMA as intermediates, ultimately leading to the formation of carbon dioxide (CO(2)) and ammonia (NH(3)).

Characterizations of denitrifying polyphosphate-accumulating bacterium Paracoccus sp. Strain YKP-9

A denitrifying polyphosphate-accumulating bacterium (YKP-9) was isolated from activated sludge of a 5-stage biological nutrient removal process with step feed system. This organism was a Gram-negative, coccus-shaped, facultative aerobic chemoorganotroph. It had a respiratory type of metabolism with oxygen, nitrate, and nitrite as terminal electron acceptors. The 16S rRNA gene sequence of strain YKP-9 was most similar to the 16S rRNA gene sequence of Paracoccus sp. OL18 (AY312056) (similarity level, 97%). Denitrifying polyphosphate accumulation by strain YKP-9 was examined under anaerobicanoxic and anaerobic-oxic batch conditions. It was able to use external carbon sources for polyhydroxyalkanoates (PHA) synthesis and to release phosphate under anaerobic condition. It accumulated polyphosphate and grew a little on energy provided by external carbon sources under anoxic condition, but did neither accumulate polyphosphate nor grow in the absence of external carbon sources under anoxic condition. Cells with intracellular PHA cannot accumulate polyphosphate in the absence of external carbon sources under anoxic condition. Under oxic condition, it grew but could not accumulate polyphosphate with external carbon sources. Based on the results from this study, strain YKP-9 is a new-type denitrifying polyphosphate-accumulating bacterium that accumulates polyphosphate only under anoxic condition, with nitrate and nitrite as the electron acceptors in the presence of external carbon sources.

Biodegradation of insecticide carbofuran by Paracoccus sp. YM3

A bacterium (Paracoccus sp. YM3) capable of degrading carbofuran was isolated from carbofuran-contaminated sludge. The strain was shown to metabolize carbofuran (50 mg L(-1)) to carbofuran-7-phenol in minimal salt medium within 6 days in which the pesticide was the only source of carbon. Carbofuran and its main metabolite were analyzed by high performance liquid chromatography (HPLC). The addition of an other carbon source led to accelerated biodegradation. The relevant degrading-enzyme was intracellular and inducible. A tobacco hypersensitivity experiment showed that YM3 could eliminate carbofuran in soils effectively and safely. This is the first report of a Paracoccus sp. that could degrade carbofuran. The present study may provide a basis for biotreatment of wastewaters and bioremediation of carbofuran-contaminated soils.

Biofiltration of trimethylamine, dimethylamine, and methylamine by immobilized Paracoccus sp. CP2 and Arthrobacter sp. CP1

A biofilter using granular activated carbon with immobilized Paracoccus sp. CP2 was applied to the elimination of 10-250 ppm of trimethylamine (TMA), dimethylamine (DMA), and methylamine (MA). The results indicated that the system effectively treated MA (>93%), DMA (>90%), and TMA (>85%) under high loading conditions, and the maximum degradation rates were 1.4, 1.2, and 0.9g-Nkg(-1) GAC d(-1). Among the three different amines treated, TMA was the most difficult to degrade and resulted in ammonia accumulation. Further study on TMA removal showed that the optimal pH was near neutral (6.0-8.0). The supply of high glucose (>0.1%) inhibited TMA removal, maybe due to substrate competition. However, complete TMA degradation was achieved under the co-immobilization of Paracoccus sp. CP2 and Arthrobacter sp. CP1 ( approximately 96%). Metabolite analysis results demonstrated that the metabolite NH(4)(+) concentrations decreased by a relatively small 27% while the metabolite NO(2)(-) apparently increased by heterotrophic nitrification of Arthrobacter sp. CP1 in the co-immobilization biofilter.

[Research advances in aerobic denitrifiers]

This paper reviewed the varieties and characteristics of aerobic denitrifiers, their action mechanisms, and the factors affecting aerobic denitrification. Aerobic denitrifiers mainly include Pseudomonas, Alcaligenes, Paracoccus and Bacillus, which are either aerobic or facultative aerobic, and heterotrophic. They can denitrify under aerobic conditions, with the main product being N2O. They can also convert NH4+ -N to gas product. The nitrate reductase which catalyzes the denitrification is periplasmic nitrate reductase rather than membrane-bound nitrate reductase. Dissolved oxygen concentration and C/N ratio are the main factors affecting aerobic denitrification. The main methods for screening aerobic denitrifiers, such as intermittent aeration and selected culture, were also introduced. The research advances in the application of aerobic denitrifiers in aquaculture, waste water processing, and bio-degradation of organic pollutants, as well as the contributions of aerobic denitrifiers to soil nitrogen emission were summarized.

[Isolation and identification of aerobic denitrifiers and dispose the wastewater of NO3(-)-N]

After domesticating activated sludge to enriched aerobic denitrifiers, 5 aerobic denitrifiers were isolated from it. The removal rates of TN were 90.4%, 91.2%, 94.6%, 95.6% and 97% by fl, f2, f3, f5 and f7, respectively. According to the physiological biochemical index, five strains of aerobic denitrifiers were generally identified as Pseudomonas sp., Paracoccus sp., respectively. The establishment of continuous flow reactor surveyed various indices. And the efficiency of nitrate nitrogen removal can reach up to 98.16%, when the reactor works smoothly. The nitrite concentration of effluent was at a low level and the maximum value was no more than 3.56 mg/L. At the same time, the efficiency of COD removal was 87.24%, which demonstrates the coinstantaneous removing of both organic and nitrate nitrogen.

Chemolithoautotrophic oxidation of thiosulfate, tetrathionate and thiocyanate by a novel rhizobacterium belonging to the genusParacoccus

Two tropical leguminous-rhizospheric strains, SST and JT 001, phylogenetically closest to Paracoccus thiocyanatus and Paracoccus pantotrophus, respectively, were isolated on reduced sulfur compounds as sole energy and electron sources. While SST had versatile chemolithotrophic abilities to oxidize thiosulfate, tetrathionate, thiocyanate, sulfide and elemental sulfur, JT 001 could oxidize thiosulfate, soluble sulfide, elemental sulfur and a relatively lesser amount of tetrathionate. Positive hybridization signals were detected for JT 001 but not SST, when their genomic DNAs were probed with DIG-labeled sulfur oxidation genes amplified from the chemolithotrophic alphaproteobacterium Pseudaminobacter salicylatoxidans KCT001. Though the new isolate SST exhibited high 16S rRNA gene sequence similarity with the monotypic species P. thiocyanatus, it was found to be considerably distinct from the latter in terms of phenotypic and chemotaxonomic characteristics. Polyphasic systematic analysis, however, confirmed that JT 001 was a strain of P. pantotrophus.

[Isolation of a monocrotophos-degrading bacterial strain and characterization of enzymatic degradation]

A monocrotophos [dimethyl (E)-1-2-methylcarbamoylvinylphosphate or MCP] -degrading strain named as M-1 was isolated from sludge collected from the wastewater treatment pool of a pesticide factory and identified as Paracoccus sp. according to its morphology and biochemical properties and 16S rDNA sequence analysis. Using MCP as a sole carbon source, M-1 was able to degrade MCP(100 mg x L(-1)) by 92.47% in 24 h. The key enzyme(s) involved in the initial biodegradation of monocrotophos in M-1 was shown to be constitutively expressed cytosolic proteins and showed the greatest activity at pH 8.0 and 25 degrees C, with its Michaelis-Mentn's constant (K(m)) and maximum degradation rate (V(max)) of 0.29 micromol x mL(-1) and 682.12 micromol (min x mg)(-1) respectively. This degrading enzyme(s) was sensitive to high temperature, but kept high activity under alkaline conditions.

Paracoccus sulfuroxidans sp. nov., a sulfur oxidizer from activated sludge

Bacterial strain LW36T was isolated from activated sludge of a wastewater-treatment bioreactor. Cells of strain LW36T were Gram-negative coccoids to short rods, 1.0-1.2x0.5 microm in size. Colonies were cream-coloured, smooth and circular. Strain LW36T was hetero-organotrophic and chemolithotrophic and was able to use reduced sulfur as an energy resource. Growth was observed at 25-36 degrees C and pH 5-10. The most abundant cellular fatty acid of strain LW36T was C18:1omega7c (64.2%). The sole respiratory quinone was ubiquinone-10. The G+C content of the genomic DNA was 61.3 mol% (Tm). 16S rRNA gene sequence analysis indicated that strain LW36T was phylogenetically related to members of the genus Paracoccus, with similarities ranging from 92.4 to 94.9%. Based on these results, it is concluded that strain LW36T represents a novel species of the genus Paracoccus, for which the name Paracoccus sulfuroxidans is proposed. The type strain is strain LW36T (=CGMCC 1.5364T=JCM 14013T).